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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 24 |
| 4 | 264 |
| 5 | 5640 |
| 6 | 151200 |
| 7 | 5722920 |
| 8 | 282868992 |
| 9 | 18371308032 |
| 10 | 1504791561600 |
| 11 | 148978034686800 |
| 12 | 18007146260231040 |
| 13 | 2528615024682544512 |
| 14 | 426310052282058252672 |
| 15 | 81830910530970671616000 |
| 16 | 18305445786667543107072000 |
| 17 | 4570435510076312321728158720 |
[1,4,24,264,5640,151200,5722920,282868992, 18371308032,1504791561600,148978034686800, 18007146260231040,2528615024682544512, 426310052282058252672,81830910530970671616000, 18305445786667543107072000, 4570435510076312321728158720] |